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SUVs Toyota RAV4 Toyota RAV4 Throttle Lag
79 messages, Last post on Aug 11, 2009 at 7:38 PM
You are in the Toyota RAV4 Forum. Your Hosts are steve_ & tidester
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Replying to: andrew17 (Oct 06, 2006 8:20 am) If you remove the battery connections for a period of time, say 15 minutes, the ECUs will need to relearn, recalibrate, some of the individual sensor parameters and that might change the vehicle "reactions" until the recalibration has completed. But thereafter.... There is some evidence indicating that following the battery disconnect procedure each and every night helps to alleviate the engine/transaxle downshift delay/hesitation for most of the next day's use. |
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Impossible to believe... Ford has the answer.....! From the new 2007 Ford Edge PR.. "The electronically shift controlled transmission also features a variable displacement pump, which matches the amount of fluid that gets pushed through the transmission to driver demand, making it more efficient." At full lift-throttle all of the FWD Toyota/lexus vehicles begin an upshift just as the engine RPM drops to idle. With the engine at idle the upshift will exhaust/use most, or possibly all, of the pressurized ATF. Now if you happen to re-apply foot pressure to the accelerator pedal just as the upshift begins the engine/transaxle ECU will "know" to delay the onset of engine until the low engine "idle" RPM can build enough ATF pressure to complete the corresponding downshift. The most obvious answer would be to increase the volume of the fixed volume ATF pump so enough pressure/flow could be provided for two sequential QUICK shifts with the engine at idle. But then most of that added volume would be bypassed, disapated as heat, as the engine RPM rises above idle. Ford's answer, apparently, is to have a variable displacement ATF pump so it can be switched to high volume when quick/SOLID shifting is required with the engine at idle. Makes me wonder if that allowed them to eliminate the ATF pressure bypass relief spring/valve also. That would REALLY increase transaxle efficiency. A second option would havre been to have an ATF pressure storage accumulator (like the ABS pumpmotor asembly). But putting one of those in an already "crowded" six-speed transaxle is probably out of the question. Anyone know if any of the newer Toyota/Lexus transaxles have either? Absent one or the other the delay/hesitation issue will undoubtedly continue. |
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In 2006 RAV4 4-cyl with 15K miles, using mid-grade or high-test gas seems to help the throttle lag situation we've experienced since day one with this vehicle. Problem's still there but not as frequent. Dealer suggested this, so they must have some clue. Any ideas, anybody? BTW, the NHTSA site has even more complaints posted but no investigations so far. 
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Replying to: fordm (Oct 27, 2006 8:17 am) Higher octane allows the engine to operate in a Taller gear ratio at a low(er) RPM without "lugging", knock/ping. So with a higher octane when you initially re-apply pressure to the gas pedal shortly after/during the lift-throttle upshift the transaxle may (more often) remain, briefly, in the "taller" gear ratio since the ECU "knows" that will not result in a seriously detrimental level of Knock/Ping. The ECU would therefore allow the DBW system to immediately begin raising engine RPM, generating additional drive torque, as a result of the new, re-applied, gas pedal pressure. So now the engine RPM is no longer at idle and should you continue to increase the pressure on the gas pedal such that a downshift is required to keep the engine in a proper, non-lugging, operating range there is now much more likelihood that there will be be enough ATF pump pressure/flow volume to accommodate the upcoming downshift. The above might also be an indication that a fairly s..l...o....w re-application of pressure to the gas pedal after a FULL lift-throttle event might often alleviate the downshift delay/hesitation regardless of octane. Whereas a quick/fast/heavy re-application would almost always result in a serious level of knock/ping absent an immediate downshift. Counter-intuitive, huh..?? Go SLOW, to GO QUICKLY...!! Okay...?? |
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Regardless of lack of mental capability of the idiot on the US throne at the moment our government is not altogether stupid. Bear with me for a moment and just briefly assume that my theory is correct that these 1999 to current MY transaxle problems have arisen out of the need to alleviate the potential for engine compression braking interferring with the anti-lock braking system. If that is the case and an investigation were to be opened the obvious conclusion would be, must be, that absent these new transaxle charactoristics all FWD or front torque biased AWD vehicles are inherently unsafe for operating on adverse, slippery, roadbed conditions. So were I the head of the NHTSA I wouldn't dare even open an investigation once Toyota informed me of the base purpose, cause, of these symptoms.
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Replying to: wwest (Oct 31, 2006 12:55 pm)  So, go slow to go fast - now wrap that in with transmission "learning" and tell me how confused the car is going to get?
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Replying to: steve_ (Oct 31, 2006 12:57 pm) Granted, these ECU's do have to "learn" the charactoristics of the individual sensors and in some cases deterministic forcing functions due to unavoidable tolerances. But I do not believe that any significant level of driver unique charactoristics "learning" is involved in the majority of these "driveability" complaints. Yes, most of these systems "watch" driver functions and according to the engineering white papers I have read will categorize each driver into one of four "bins" within a few seconds of first putting the vehicle in motion, and then with more time will refine the characterization into one of sixteen "bins". But all of the learning regarding individual driver unique charactoristics is ERASED each and every time the engine is (re)started.
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Replying to: wwest (Oct 31, 2006 1:43 pm) |
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Assuming the new shift pattern upshift technique is to help alleviate accidents due to loss of directional control arising for engine braking, why not just have a SNOW mode that can be activated by the driver, by a rain sensor, or if the OAT hovers around or below freezing. Upon a full lift-throttle event in SNOW mode the transaxle would remain in the same gear ratio but the engine RPM, via DBW, would not be allowed to fall enough to provide a significant level of engine braking to the driven wheels, front, rear, or ALL. Absent being in SNOW mode the shift patetrn could be the same as it was pre-2000. |
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Replying to: raviola4 (Oct 06, 2006 8:47 am) Now the stereo is going haywire. Sometimes it does not respond to the on/off button, and sometimes the display will not come on even though the controls work. Is there some kind of electronic problem that would affect both throttle control and the stereo? Seems unlikely but am curious.
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